Late glacial — early holocene palaeosalinity in Alberta,Canada — climate implications     

Michael Hickman  Charles E. Schweger 《Journal of Paleolimnology》1993,8(2):149-161

Palaeolimnological and palynological records from climatically variable central Alberta, Canada, document periods of hypersaline lake conditions indicative of late glacial and early Holocene drought. The sensitivity of palaeolimnological indicators for inferring palaeoclimates is examined by comparing records from two sites at opposite ends of the regional precipitation gradient. Palaeosalinity is identified by the presence of Ruppia pollen, a hypersaline aquatic plant not presently growing in either lake, and diatom assemblages comprising both saline epipelic and planktonic species. Goldeye Lake (52° 27 N; 116° 12 W), in the relatively moist Rocky Mountain Foothills remained saline from its inception before ca 14500 years BP until ca 10400 years BP by which time pioneering forests had replaced tundra vegetation; however, freshwater planktonic diatoms dominated ca 12500 to 11500 years BP. However, dating problems endemic to the Foothills region make this chronology only tentative. Moore Lake (54° 30 N; 110° 30 N), in dry, east-central Alberta contained Ruppia only between ca 9000 and 6000 years BP. Freshwater diatoms dominated until ca 10000 years BP when they were succeeded by taxa characteristic of saline water. The lake remained saline until ca 6000 years BP. The late glacial period of palaeosalinity at Goldeye Lake occurred because the lake was surrounded by Cordilleran and Laurentide glacial ice, and therefore, cut off from moisture sources until the early Holocene by which time significant ice recession had occurred. Factors causing the second period of salinity remain unknown at this time. In contrast, by the early Holocene, Moore Lake was influenced by drought caused by high summer insolation induced by orbital fluctuations. Freshwater conditions were maintained through the Holocene in the Foothills region of west-central Alberta, but occurred consistently only over the last 4000 years in central and east-central Alberta. The warmer, drier climate during the early Holocene did affect lake levels in at least one headwater Foothills lake (Fairfax Lake — 52° 58 N; 116° 34 W). The severity of the drought increased in an easterly direction across the province.This publication is the fourth of a series of papers presented at the Conference on Sedimentary and Palaeolimnological Records of Saline Lakes. This Conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr. Evans is serving as Guest Editor.  相似文献   

亚洲热带山地垂直植被带对晚第四纪气候变化的响应   总被引：5，自引：2，他引：3  

郑卓 《地理研究》1999,18(1):96-104

过去一直认为热带低海拔地区晚更新世冰期的地表气温基本维持不变。孢粉分析、树线等研究结果证明,从南半球的新几内亚和赤道附近的苏门达腊,一直到我国的热带山地在末次盛冰期垂直植被带下降了500m～1600m不等。植被带的下降不仅仅与温度变化有关,其他的综合因素如高海拔紫外线辐射、大气CO₂浓度等都可能共同影响垂直植被带的分布。综合研究认为,整个亚洲地区年均温度平均下降约4℃的结果与热带非洲和美洲基本一致,并与近两年来热带海洋表层水温的研究结果和近期的气候模拟结果相吻合。  相似文献   

豫西南晚白垩世红层时代厘定及其意义   总被引：1，自引：0，他引：1  

冯祖杰  周世全  李占扬 《地质通报》1999,18(3)

研究区位于豫、鄂、陕三省相邻地带,在秦岭造山带后造山阶段构造体制转换过程中,形成了李官桥、滔河、西峡、夏馆、五里川、召北等一系列近于平行的断陷盆地,盆地内分别沉积了１０００～４０００ｍ的陆相碎屑沉积。根据恐龙蛋、轮藻、孢粉、介形类及一定数量的恐龙骨骼化石、同位素年龄等,将盆地内红层的时代归属为晚白垩世,并对每一盆地红层进一步作了详细划分。  相似文献   

European Climatic Response to Millennial-Scale Changes in the Atmosphere–Ocean System during the Last Glacial Period     

María Fernanda Snchez Goi  Jean-Louis Turon  Frdrique Eynaud  Sandra Gendreau 《Quaternary Research》2000,54(3):394

Pollen, foraminifer, dinocyst, and coarse lithic high-resolution analyses and δ¹⁸O measurements have been carried out for the last-glacial section of marine core MD95-2042 located near the southwestern margin of the Iberian Peninsula. The pollen data indicate a high frequency of vegetational changes on the adjacent continent during this period, suggesting a climatic variability very similar to that of the Dansgaard-Oeschger cycles recorded by the Greenland ice cores. The detailed direct correlation of the terrestrial and marine proxy data from core MD95-2042 indicates a three-phase pattern of Heinrich events in land and ocean environments. The first and last phases of the H5 and H4 events are characterized by a mild and humid climate in southwestern Europe, probably associated with the European origin of the ice-rafted detritus. The middle phase exhibits a cold and dry climate in Iberia linked with the maximum input of ice-rafted detritus. This phase seems to correspond with the Laurentide ice-sheet surges. Between the Heinrich events, several cold and dry periods on land are correlated with stades of the Dansgaard-Oeschger cycles. The impact of the Dansgaard-Oeschger stades in southwestern Europe seems to be preferentially connected to the cold winter air masses reaching this mid-latitude region.  相似文献   

Paleoclimatic Changes During the Last 2.5 Ma Recorded in the Kathmandu Basin, Central Nepal Himalayas     

Rie Fujii  Harutaka SakaiWT  ”BX 《地学前缘》2000,(Z1)

PALEOCLIMATIC CHANGES DURING THE LAST 2.5Ma RECORDED IN THE KATHMANDU BASIN, CENTRAL NEPAL HIMALAYAS  相似文献   

辽宁西部义县组被子植物花粉的首次发现   总被引：15，自引：4，他引：11  

王宪曾  任东 《地质学报》2000,74(3):265-272

对辽宁西部晚侏罗世义县组中的孢粉植物群进行了系统研究,首次发现了目前为止世界上最古老的被子植物花粉化石。该花粉植物群可分为三大类,即无孔粉类、原始单远极沟粉类和原始三沟粉类。该发现表明在晚侏罗世原始被子植物已经存在,并且已呈现出多类型特点。义县组中被子植物花粉的新发现为研究被子植物起源问题提供了新的化石依据。  相似文献   

Records of aquatic pollen and sediment properties as indicators of late-Quaternary Alaskan lake levels     

Mary E. Edwards  Nancy H. Bigelow  Bruce P. Finney  Wendy R. Eisner 《Journal of Paleolimnology》2000,24(1):55-68

We investigated whether techniques developed to evaluate qualitative lake-level changes in the temperate zone can be used in sub-arctic and arctic Alaska. We focused on aquatic pollen records and sediment properties (loss-on-ignition and magnetic susceptibility) from centrally-located sediment-surface samples and cores, as these are the most commonly reported data in the literature. Modern aquatic pollen values are generally low (< 5%) and may be zero, even in lakes with abundant aquatic macrophytes. Greater diversity and higher values of aquatic pollen are likely at depths < 5 m, but pollen is found in depths up to 15 m. It is absent at depths > 20 m. Spores of Isoetes and Equisetum and Pediastrum cell-nets, when present, tend to be widely distributed, even in deep water. At Birch Lake, interior Alaska, trends in aquatic taxa and sediment characteristics for the last ca. 12,000 ¹⁴C yrs recorded in a single, deep-water core reflect the same water-level changes as do transect-based lake-level reconstructions - if modern distributional characteristics of pollen and spores are taken into account. The lake rose from extremely low levels at ca. 12,000 ¹⁴C yr B.P. After a period of fluctuation, it rose to a relatively high level by ca. 8000 ¹⁴C yr B.P. and then stabilized. A preliminary survey of aquatic pollen trends from other lake-sediment records suggests that the period ca. 11,000-8000 ¹⁴C yr B.P. may have seen relatively low lake levels in north-western and interior Alaska and high levels thereafter. Changes in aquatic pollen and sediments are evident in north-eastern interior lakes at the same time, but they are more difficult to interpret. Aquatic pollen productivity in Alaskan lakes may partly depend on factors other than water depth (e.g. temperature, pH, nutrient status, or length of the ice-free season). An Alaska-wide reconstruction of late-Quaternary lake levels based on extant single-core data would be best done after further study of contributing factors that may control sediment properties and aquatic pollen distribution.  相似文献   

燕山地区花粉散布特征研究   总被引：1，自引：0，他引：1  

许清海  阳小兰  梁文栋 《地理与地理信息科学》2000,16(4):54-58,62

燕山南部花粉散布特征研究表明 ,空气中的花粉反映的是植物花期的季节性变化 ;表土花粉是植物多年花粉散布的混合 ;冲积物花粉与空气中和表土花粉显著不同 ,是取样点上游表土花粉的混合 ,与取样点周围植被关系较小。因此 ,根据冲积物花粉恢复古植被 ,反映的是整个流域的植被面貌 ,而不是某一点的植被特征  相似文献   

南海南部末次冰期以来的孢粉记录及其气候意义   总被引：24，自引：0，他引：24       下载免费PDF全文

李逊  孙湘君 《第四纪研究》1999,19(6):526-535

本文通过分析南海南部１７９６４柱状样的孢粉记录,重建了该地区２６０００ａＢ．Ｐ．以来的植被和气候变化历史。南海南部末次盛冰期时高山雨林的范围可能是现在的２～３倍,表明气温明显下降;从末次盛冰期到冰消期,巽他陆架一直为热带低地雨林及红树林占据,表明在此期间湿度没有明显变化,但存在着千年级的准周期波动。这种波动一直持续到全新世中期。本地区在２０００ａＢ．Ｐ．以来芒萁孢子大量增加,一些高山雨林的成分重新出现,可能与人类活动所导致的低地植被的破坏有关。  相似文献   

Peatland Initiation During the Holocene in Continental Western Canada   总被引：4，自引：0，他引：4  

Linda A. Halsey  Dale H. Vitt  Ilka E. Bauer 《Climatic change》1998,40(2):315-342

Today, the southern limit of peatlands in continental western Canada is largely limited by thermal seasonal aridity, although physiographic parameters of substrate texture, topography, and salinity also exsert important controls on the presence and absence of peatlands. Factors that control peatland distribution today also operated in the past, thus the initiation of peatlands during the Holocene was mainly limited by aridity and physiography. Calibrated radiocarbon dates of basal peat deposits from 90 locations across continental western Canada indicate that peat formation began approximately 8,000 to 9,000 years BP in nucleation zones along the upper elevations of the Montane region of Alberta and in northern Alberta uplands after an initial deglacial lag. Predictions of maximum early Holocene summer insolation by climate simulations provide a mechanism for limiting peatland establishment during the early Holocene. From 6,000 to 8,000 years ago, peat formation in continental western Canada expanded eastwards into Manitoba responding to decreases in summer insolation. Peatland expansion during the early Holocene was more extensive in Alberta than in Manitoba in response to a southwesterly shift in the Arctic front. The displacement of the Arctic front allowed for more frequent incursions of moist Pacific air into Alberta while limiting it in Manitoba. After 6,000 years BP, the trend of southeasterly peatland expansion continued. Peatlands are youngest in the southern Boreal Forest and Aspen Parkland Region as well as in the lower elevations of the Peace-Wapiti River drainage basin, forming over the last 3,000 to 4,000 years. Peatlands are also young in the lower elevations of the Hudson Bay Lowlands where peat initiation has been limited by timing of emergence from glacial rebound. The spatial and temporal distribution of peatland initiation during the Holocene is verified by existing pollen records and corroborates some simulated climate models.  相似文献